Ice build-up on the surfaces of such things as sign faces, signal transmission lines (e.g., telephone and electrical cables), automobiles, railroad cars, aircraft, heat exchange equipment, ice manufacturing facilities, buildings, transportation signs, roofing, snow removal equipment and the like presents a long recognized problem. While it is highly preferred to prevent ice build-up on such surfaces, no truly effective method of doing so has yet been found. Consequently, most techniques for resolving this problem involve techniques for the removal of an accumulation of ice from surfaces.
Thermal removal has been suggested. However, this technique requires a significant expenditure of energy and is generally ineffective where the ambient temperature is low.
Another technique involves the application of a silicon-containing coating to surfaces. However, this technique is not entirely satisfactory. U.S. Pat. No. 2,567,804 describes the use of a multilayer coating in which an organosilicon halide is first applied to the surface and then a prepolymerized silicone is applied thereover. The prepolymerized silicone has a viscous oily or greasy consistency. This approach suffers from the disadvantage of requiring the application of two separate layers of material. Additionally, the greasy top layer is aesthetically unpleasing and unsuitable for applications where repeated hand contact is to be made.
U.S. Pat. No. 3,522,202 describes the use of a composition consisting of (a) a dimethylpolysiloxane-containing terminal silicon bonded hydroxyl groups, (b) a methyl hydrogen polysiloxane, and (c) a methylphenylpolysiloxane containing terminal hydroxyl groups. This composition is applied from an organic solvent. As such, it not only presents potential pollution problems, it also necessitates the use of expensive solvent recovery systems. The use of solvent also adds a potential safety hazard.
U.S. Pat. No. 3,579,540 describes the use of a composition comprising a mineral acid, a solvent and an alkylpolysiloxane to render a nonporous surface water repellent. This composition also presents pollution and safety problems in its application. Additionally, however, the use of mineral acids presents problems of corrosion and also depolymerization of the polysiloxanes employed.
U.S. Pat. No. 4,271,215 discloses the application of a coating composition comprising a carboxy-functional siloxane fluid, an organic titanate, and a volatile diluent to a water-impermeable surface to give it ice release properties. This composition also presents pollution and safety problems in its application.
U.S. Pat. No. 4,301,208 discloses the application of a coating comprising a block copolymer of polycarbonate and dimethylpolysiloxane containing a silicone oil to render a surface capable of releasing ice. This composition is applied from solvent and accordingly presents the above-identified pollution and safety problems. Furthermore, it is a thermoplastic composition and the literature indicates that it has poor adhesion to some substrates. Still further, the resulting material is only physically crosslinked. This type of crosslinking is reversible unlike that of the compositions employed in the present invention.
U.S. Pat. No. 4,636,324 discloses the use of a composition comprising 40 to 99.6 weight % of an organopolysiloxane, 0.2 to 30 weight % of an alkali metal salt, and 0.2 to 30 weight % of a liquid and/or a solid paraffin. U.S. Pat. No. 4,448,919 discloses the use of a composition comprising from 70 to 99.8 weight percent of an organopolysiloxane and 0.2 to 30 weight percent of an alkali metal salt. The alkali metal salts employed in the '324 and '919 compositions can be leached out of the compositions, decreasing their ice-releasing capabilities and causing corrosion problems.
German Offenlegungsschrift DE 3451100 A1 describes the use of a composition containing .varies.- and .omega.-dihydroxypropyl(dioganosiloxanes), alkyl-triacetoxysilanes, fillers, pigments, solvents, and optionally .varies.,.omega.-bis(trimethylsiloxy)poly(dimethylsiloxane). This composition employs a silanol functional polysiloxane. In addition, it is applied at a thickness of 1.5 mm. This corresponds to a coating weight of approximately 1500 g/m.sup.2 and is significantly heavier than is employed in the present invention.
Yet another approach that has been tried is the use of polytetrafluoroethylene to reduce the adhesion of ice on surfaces. Again, however, this approach has not proven to be entirely satisfactory. This technique requires the application of a coating or layer of a fairly expensive polymer and provides a surface which, at best, provides only marginal ice release capabilities.
U.S. Pat. Nos. 4,504,645 and 4,533,575 disclose the use of latently curable organosilicone release coating compositions which are applied as a thin layer (e.g. 1 g/m.sup.2) to provide release from an adjacent adhesive layer. Thin coatings of this type do not provide suitable ice release capability.
International Application No. PCT/GB 88/00285 discloses a system for releasing ice from a surface which employs a two component polymeric coating on a surface. The first component is not removable from the surface by solvents. The second component is dissolved or dispersed homogeneously in the first component but is not bonded to the first. The first component is physically or chemically grafted to the surface and more preferably contains a reactive end or side group. The second component preferably has an oily, waxy or greasy consistency. Mineral oils, organic polysiloxanes, fluorinated polymers, ethylene/propylene copolymers and polyurethanes are said to be useful as the first and second components.
U.S. Pat. No. 2,494,920 describes the application of a coating containing an organopolysiloxane, a heat resistant inorganic filler, and a peroxide (such as a diacyl peroxide). The composition is applied to a substrate and then baked until it has reached a temperature of 180.degree. C. for two minutes. This composition is said to render surfaces water repellent. However, the use of fillers tends to render the composition opaque and hence unsuitable for many applications. Moreover, the use of high temperatures to polymerize the coating is undesirable.